In a conventional differential device employing a bevel gear, not only is it impossible to avoid the occurrence of a teeth-rattling noise, which are characteristic of bevel gear meshing, but since the number of simultaneously-meshing teeth are only some of the total number of teeth, the torque is also borne only by some of the teeth, and there is room for improvement in terms of strength and durability.
A differential device employing a ball mechanism as in Patent Document 1 is known, but since in this device, a plurality of balls are slidably held by a plurality of radial elongated holes of the center plate, opposite side parts, exposed through the elongated holes, of these balls are rollably engaged with transmission grooves of left and right disk plates, when there is differential motion of the left and right disk plates, the balls move on the three, that is, the elongated hole and the left and right transmission grooves, at the same time, and the frictional resistance of the ball at that time therefore causes a large power loss, thus affecting the engine fuel consumption performance.
Furthermore, a cycloid type transmission mechanism as in Document 2 in the related art is also known, but this is a simple transmission mechanism, and its application as a differential device is difficult.